Soil suitability classification by farmers in southern Rwanda

GEODERt’MA Geoderma 7.5 (1997) 75-87 Soil suitability classification by farmers in southern Rwanda Emmanuel Habarurema a*b,1,Kurt G. Steiner a,b32 ’ Uniuersite' National zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM du Rwanda, Butare, Rwanda h Institut des Sciences Agronomiques du Rwanda, Rubona, Rwanda Received 11October 1995; accepted 12 September 1996 Abstract In mountainous areas soil characteristics may vary within short distances due to the relief. The scale of most soil maps is usually too coarse to take these variations into consideration, thus limiting their usefulness for technology development and extension. Field studies in southern Rwanda revealed that farmers have a profound knowledge of their soils, and classify soils for their own needs. The classification is based on the identification of different soil types according to their agricultural potential and tillage properties. The main criteria applied are: fertility (productivity), depth, structure and colour. Nine major soil types are distinguished. More experienced, older farmers use additional parameters such as indicator plants, texture, consistence and parent material and are capable of further subdividing these types into sub-classes and groups. In the three agro-ecological zones of the study area, situated in different districts, farmers always applied the same names. No clear correlation was found between soil types according to farmers’ classification and soil types classified according to Soil Taxonomy. Farmers and scientists appraise soil in different ways. While farmers are interested in soil productivity and appropriate management practices, they take only the topsoil or the arable layer into account. Soil scientists, on the other hand, are also interested in the deeper-lying soil horizons and soil genesis. In addition, farmers’ classification is based on local soils and farmers’ objectives. Thus names may vary from one region to the other, making comparisons on a (inter)national level impossible. Farmers’ soil classes correspond to soil suitability classes, and may therefore be useful for land evaluation systems. The use of vernacular names facilitates exchange between farmers, extension I Present address: UNHCR-Camp, Bukavu, Zaire. ’ Present address: GTZ, P.O. Box 5180, 65726 Eschbom, Germany. Tel.: +(49)6196-793287/797378. Fax: +(49)6196-797413. E-mail: gtz-boden@geod.geonet.de 0016- 7061/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved PII SOO16-7061(96)00078-X 76 E. Habaruremu. K.G. Steiner/Geoderma 75 (19971 75-87 workers and researchers. In order to make practical use of farmers’ knowledge, further investigation is required to establish whether farmers in other parts of Rwanda apply the same names and in the same way. Keyords: soil classification: farmers’ system: indigenous knowledge: soil management; Rwanda 1. Introduction Countless generations of farmers have tilled the hills of Rwanda. Due to an ever increasing population, farm sizes have decreased and farmers have been forced to intensify their production systems. Permanent cropping and organic manuring have allowed for population concentrations of over 700 persons/km2 in some agricultural areas, the national average amounting to 380 persons/km’ usable land in 1989 (Cambrezy, 1984; Nduwayezu, 1990). Thus it is not surprising to discover that the farming community possesses a considerable body of knowledge especially in soil management (Steiner, 1984). What is surprising, however, is the fact that this knowledge has not been tapped at all, whether by agricultural research or by extension. even though everyone speaks the same national language, Kinyarwanda. It is only recently that farmers have been invited to participate in research and technology development, at least by some research teams and extension services (Sperling and Steiner, 1992; Sperling et al., 1993). All this, of course, is not unique to Rwanda. Agricultural research and extension in mountainous Rwanda face tremendous difficulties due to a highly diversified environment. Soils, rainfall and temperature vary considerably, even within relatively short distances. Soils, in particular, may change from field to field in relation to topography and toposequences (Steiner et al., 1994). The soil map scales of semi-detailed surveys are too small to take these differences into account, but they nevertheless are used to determine soil management and suitability for crops. All this renders the definition of recommendation domains difficult. Standard recommendations are hardly suitable; instead farmers have to adapt general messages to their farming conditions by running their own trials. This necessitates close collaboration and an intensive dialogue between farmers, researchers and extensionists (Steiner, 1987). Farmers have to contribute their specific local knowledge. 2. Scientific soil classification systems technology development and extension (used in Rwanda) and their limits for Soils have been studied and described and, at least for some regions, soil maps have been drawn since early colonial times. Nearly every new development project undertakes some pedological studies in order to describe soils in the project region. Different classification systems are used: the FAO world soil legend (FAO, 1988), the USDA Soil Taxonomy (Soil Survey Staff, 19941, the French soil classification (CPCS, 1967; Duchaufour, 19911, and the INEAC soil classification (Sys et al., 1961). The importance of these studies and the value of the database created is not questioned; however, it is E. Habarurema, K.G. Steiner/Geoderma 75 (19971 75- 87 17 also obvious that their usefulness for technology development and extension is limited, especially with regard to the genetically orientated soil classifications. What is needed by farmers and extensionists is not so much soil classification but rather land evaluation (Sys and Van Ranst, 1992), preferably using less sophisticated terms for specific soil management and cropping systems. These systems should allow the identification of soil types or classes by relatively simple means, such as yields (fertility), indicator plants and slope position, as well as simple soil characteristics (smell, colour, texture, depth, etc.), to facilitate real dialogue between farmers, extensionists and researchers. 3. Farmers’ soil classification Systematic studies of farmers’ knowledge of soil and their soil classification and land evaluation systems have been carried out in only a few countries, for instance in Nigeria (Osunade, 1988>,Indonesia (Grobben, 1992), Burundi (Rurihati, 1993), Zambia (Sikana, 1993) and Burkina Faso (Schutjes and Van Driel, 1994). Even though most national researchers and extension workers come from farm households, they make little use of local knowledge of soil. The meaning of names given to certain soil types is no longer understood. Due to formal training, indigenous knowledge is considered inferior, without any significance for research and development. The same situation prevails in Rwanda. Therefore attempts to use local soil names for site description in on-farm experimentation failed (Steiner et al., 1994). In a preliminary study which had the objective of defining the variability of crop yields in relation to topography, Bellemakers et al. (1991) found that farmers distinguish seven different soil types. These soil types differ in fertility, texture, water retention capability and suitability for certain crops. The objective of the present study was to investigate: (a> whether the vernacular names given to soil types by farmers in parts of Southern Rwanda are applied in a systematic way and by what criteria soils are characterised; (b) whether vernacular soil types could be correlated to soil types, classes or orders of scientific classification systems such as Soil Taxonomy and to what extent the soil names could be used in farming systems research and extension in order to facilitate dialogue with farmers. 4. Study area and methods The study was conducted in 3 administrative districts (Ruhashya, Mugusa and Ntyazo) of Southern Rwanda, each representing a different agro-ecological zone: Plateau Central, Dorsale Granitique and Mayaga (Delepierre, 1974). The objective of an initial exploratory survey was to identify criteria used by farmers to classify their soils and to describe soil levels distinguished by farmers. In each district 40 farmers, in total 120 farmers, were selected in collaboration with the extension service. Farmers were interviewed, individually or in small groups, on their fields thus facilitating communication. 78 E. Habarurema. K.G. Steiner/Geoderma 75 (lYY71 75-87 After evaluation and synthesis of the data a second survey was conducted, with the objective of verifying and refining the definition of soil classes. In connection with other ongoing studies, investigations were conducted into whether there are links between toposequences and soil types. Further, it was attempted to establish a possible hierarchy of levels. Only expert farmers, mainly older men, ten in each zone, were chosen for the second survey. Farmers were interviewed individually in their fields in a guided conversation without using questionnaires. In an attempt to link indigenous and scientific knowledge systems, possible correlations were sought between well-defined local soil levels and the USDA land capability classification (Landon, 1991). About 50 reference points of the national soil map (Birasa et al., 1992) situated in the study area were identified and the classes of the soil map compared with farmers’ classes. In addition, one or two profile pits were examined for each major vernacular soil level. The position of the soil profile on the toposequence. the type of slope, the type of landscape and of vegetation were recorded. The morphological characteristics of soil horizons were described and horizons sampled in accordance with Soil Taxonomy procedures (Soil Survey Staff, 1994). The soil samples were analysed at the National University, Butare, according to the guidelines of the FAO (1988). 5. Results and discussions Soil scientists distinguish five pedogenetic factors: parent material, topography. climate, biology and time. All of these factors, except time, were mentioned directly or indirectly by farmers during the discussions. Farmers’ knowledge of soil varies widely. It is mainly the older farmers who have a profound knowledge of their soils and use this knowledge in their decision-making. Younger farmers often know very little of soils and factors influencing soil productivity probably due to absence from farm because of schooling and off-farm work (high land pressure) as well as little interest in traditional knowledge of farming. 5.1. Criteria applied by farmers ,for classifying their soils Farmers in the three agro-ecological zones use certain soil properties and site characteristics (Table I) to clearly distinguish 9 soil types. Criteria used for classifying soils are: fertility (productivity), indicator plants (in fallow vegetation), depth. structure, texture (presence of stones and gravel), colour, consistence, drainage and subsoil characteristics. Fertility is the principal criterion used by all farmers, followed by depth, structure and colour. During the discussions farmers mentioned a number of processes and actions, which they know influence certain soil properties (Table 21, for example soil erosion, topography and manuring. Thus farmers see the soil as dynamic and try to identify the causes (pedogenetic factors, processes and their impact), but only few are able to express the interactions of pedogenetic factors and processes. E. Habarurema, K.G. Steiner/Geoderm 75 (1997) 75- 87 79 I Table Soil and vegetation criteria applied by farmers to distinguish (percentage) of farmers using them Criterion (Chemical) Description, indicators of the criteria and number Used by farmers % crop development, yields. fallow vegetation, content of soil organic matter 100 Depth depth of developed soil, depth of tillage, part of soil that can be exploited by plant roots 86 Texture and stoniness contents of clay, loam, sand, gravel, stones, underlying rocks, ease of tillage and wear of hoes, determined by eye and fingers 83 Colour determined 73 Consistence extent to which soil sticks to hoe and hand, ease of tillage and wear of hoes, determined by eye and fingers 43 Drainage determined while tilling the soil 37 Fallow vegetation indicator plants used for choice of crops and determination of necessary fallow period 30 Structure form and stability of clods formed when tilling, determines ease of tillage 20 Subsoil soil layer becoming visible during profound tillage, or by erosion processes on slopes obstacle for plants roots and water infiltration 15 5.2. Fertility soil types, explanation Differentiation of by eye soils by relief and erosion Farmers know that soil fertility and consequently soil types are closely related to relief, expressed as form of the slope (convex or concave) or position on the slope. On eroded hill tops, on steep slopes and convex slopes, shallow and stony soils, Uruseny i, dominate, while on the flat tops of hills (plateaux), concave slopes and feet of hills deep soils with a fine texture, Urunombe, prevail. The valley bottoms are covered with dark or greyish colluvial and alluvial soils (Urubumba) with mostly fine texture as well. Table 2 Pedogenetic factors and their impact on specific soil properties Factor Topography Position on slope Parent material Erosion by water Tillage Organic manuring 41 21 14 100 51 59 as seen by % of Rwandan farmers interviewed Depth of topsoil Colour Texture and stoniness Consistence 66 46 0 83 80 - 6 0 10 43 73 13 0 21 70 86 - 3 0 0 16 3 53 80 Table 3 Farmers’ appraisal E. Habaruremu. of soil management K.G. Steiner/ practices Cemderma 75 (19971 75-87 and their impact on soil degradation Element Mentioned by 0 farmers (n = 30) Frequency of tillage Insufficient organic manuring Lack of fallow Erosion by water Inappropriate tillage Unsuitable crops No effective soil conservation practices Overexploitation (soil mining) Inappropriate crop rotation Overgrazing and deforestation 80 80 66 23 16 IO IO 6 6 6 Farmers are aware of the selective results of soil erosion, leaving behind gravelly to stony soils and forming deposits of loamy or clayey soils on the flatter parts of the slope, concavities or hill foot, and finally on the valley bottom. Soil erosion was quoted by all farmers, its main impact being on soil depth and texture, especially stoniness. This is in contradiction to survey results of other authors (Schiirg, 1993; Steiner et al., 1993), who reported that soil erosion was never mentioned by farmers as a constraint or cause of declining soil fertility. According to Kiinig (1992) farmers are only conscious of erosion where already shallow soils and obviously low yields appear but not of the process of sheet erosion. The awareness of the process of soil erosion consequently depends on the steepness of the slopes thus varying between different regions of Rwanda. 5.3. Management ,fuctors enhancing soil degradation Farmers are aware of inappropriate soil management enhancing soil degradation. They see frequent tillage and insufficient rates of organic manure as the major causes for declining soil fertility (Table 3) besides the lack of fallows due to land shortage. Fallowed fields formerly served as pasture for cattle which in their turn produced manure for cropped fields. The disappearance of fallows and consequently the reduction of livestock not only led to more frequent hoeing but also to declining manure application and increased soil erosion. Hoeing has not only a negative effect because of soil disturbance and enhanced decomposition of soil organic matter, but mainly by the way fields are tilled. Fields are mostly tilled in the same direction, i.e. downslope. The soil is pulled down the slope with the hoe, removing the soil from the upper part and accumulating it on the lower part of the field, thus forming progressive terraces, while the upper parts of the fields become unproductive. Even though farmers realize this negative effect, they see no alternative, as hoeing downslope is the only practical way of tilling steep slopes. Farmers know that soil management has to be adapted to the type of soil, i.e., heavy loamy or clayey soils need to be treated differently from light sandy soils. The key factor is the content of organic matter as major source of plant nutrients, and conse- E. Habarurema,K.G. Steiner/Geodema 75 (1997) 75- 87 Table 4 Farmers’ crops assignment according 81 to the 9 soil types Soil type Farmers’ perception Urusenyi high fertility, sandy, very well drained (summary) bean, cassava Principal crops Urubuye variable fertility, sandy gravel, very well drained no specific crops Igisbonyi low-medium potato, sorghum, maize Ikigwagwa low fertility, sandy gravel, very well drained no specific crops (pasture) Umkurwe low fertility, loamy-clayey, no specific crops (pasture) Urunombe medium-high fertility, loamy-clayey, moderate permeability bean, sorghum, banana, sweet potato Umusenga medium-high sweet potato, sorghum Mugugu low fertility, loamy, well drained sweet potato, soya, cassava Urubumba variable fertility and texture, low permeability no specific crops fertility, loamy, well drained insufficient permeability fertility, loamy, moderate permeability quently organic manuring, especially with farmyard manure, is regarded as the principal soil-improving practice. 5.4. Adaptation of crop rotations and/or associations to certain soil types Certain crops are better adapted to certain soil types than others (Vandenput, 1981) and consequently farmers choose their crops according to soil type (Table 4). In practice, of course, the availability of certain soils is limited, obliging farmers to make a second best choice. Beans, an important part of the diet, maize, sorghum and bananas are considered to be demanding crops, requiring the best soils and organic manuring, whereas sweet Table 5 Subtypes of soil profiles of the Urusenyi (Insenyi) type Name of subtype Parent material Physical properties Typic Urusenyi granite, quarzite, or ferruginous schist sandy to loamy, with gravel, shallow to deep, greyish to dark Urusenyi rw’urubuye as Typic Urusenyi sandy, gravelly loam, rich in gravel and stones Urusenyi rw’igishonyi scbist/phyllite as Typic Urusenyi Urusenyi rw’ikigagwa feldspathic Urusenyi rw’urukurwe as Typic Urusenyi as Typic Urusenyi, Urusenyi rw’urunombe as Typic Urusenyi sandy loam, less gravel Urusenyi rwa kokobe as U. rw’urukurwe, but presence of plinthite as Typic Urusenyi but colour varying from red to yellow micaceous schist as Typic Urusenyi but reddish 82 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA E. Habarurema, K.G. Steiner/ Geodenna 75 f 19071 75- 87 Table 6 Subtypes of soil profiles of the Urunombe (Inombe) type Name of subtype Physical properties Typic Urunombe loamy to clayey, sticky, low permeability, Urunombe rwa mugugu as Typic Urunombe, but with oxic characteristics Urunombe rw’umusenga as Typic Urunombe, but loamy and brown Urunombe as Typic Urunombe. but loamy, gravel rw’urusenyi brown to red, no oxic characteristics potato and soya are considered to be less demanding and produce even on less fertile soils. Cassava produces best on fertile soils, but is mostly grown on very degraded slopes where it still produces a crop over one or more seasons. Consequently crop rotations including beans, maize and sorghum are preferably planted on soils of the Urusenyi type, regarded as fertile. 5.5. Placing farmers’ soil types into a hierarchy A closer examination of farmers’ land evaluation levels reveals that there are only three major soil associations: Insenyi (plural form of Urusenyi), Znombe (plural form of Urunombe) and Imbumba (plural form of Urumbumba). Insenyi regroups soils of a sandy-skeletal, sandy and sometimes loamy texture. Inombe are soils of loamy and clayey textures, while Zmbumba is not clearly defined. Imbumba signifies soils of valley bottoms, the texture of which varies considerably from sandy to clayey. They are colluvial or, in large valleys, alluvial in origin. Experienced, old farmers can subdivide the above-defined soil types further into subtypes (Tables 5 and 6). For the more common soil types such as Urusenyi, Urunombe and Urubumba up to 8 subtypes and 2 to 3 further subdivisions were mentioned. The principal criteria for subdividing Urusenyi Table 7 Subdivisions of some frequent subtypes Specific properties Subtype Urusenyi rw’urukurwe Urusenyi rw’urunombe Typic Uronombe Urunombe rw’urusenyi Typic Urusenyi rw’urukurwe Urusenyi rw’urukurwe rwa kokobe red to yellow, developed in hydromorphic sites Typic Urusenyi rw’urunombe Urusenyi rw’urunombe rwa mugugu oxic characteristics Typic Uronombe Typic Uronombe rwa rutsima Typic Uronombe rwa bukara hard good structure, plastic and compact hard good structure, compact Typic Urunombe rw’urusenyi Urunombe rw’urusenyi rw’urukurwe Urunombe rw’urusenvi rw’igishonyi hydromorphic shallow soil E. Habarurem, K.G. Steiner/Geoderma 75 (1997) 75- 87 83 and Urunombe types are: parent material, texture, structure, colour, profile depth and underlying rocks. The names of subtypes are composed of the name of the main type completed with an adjective. While the main types are used in the same sense in all Table 8 Correspondence Soil characteristics and classification between farmers’ and scientists’ classification ’ of soil shown on the example of 6 soil profiles Soil 1 2 3 4 5 6 Farmers system Urunombe urusenyi Urunombe mugugu profile 1 Urunombe mugugu profile 2 Urunombe umusenga Urunombe typical Urusenyi typical Soil Taxonomy Inceptisol Oxic, Ultic Humitropept Inceptisol Oxic Sombritropept Inceptisol Oxic, Ultic Sombritropept lnceptisol Andic Humitropept Ultisol Typic Tropudult Inceptisol Fluventic Eutropept INEAC class Ferris01 slightly ferallitic Ferris01 slightly ferallitic Ferrisol ferallitic drainage medium good medium good medium medium O-30 clayey sand o-45 clayey sand O-30 clayey sand O-30 clayey sand O-15 sandy clay 2SYR3/4 4.0 9.6 43 2.82 2.5YR3/4 4.5 12.1 28 1.67 2.5YR4/4 4.8 11.2 38 2.97 lOYR3/2 5.9 8.0 63 0.00 5YR3/3 6.1 20.8 29 0.02 O-60 clayey sand abundant lOYR2/1 6.2 14.4 54 0.05 30-60 clayey sand 45-60 clayey sand 30-50 sandy clay 30-75 clayey sand 15-55 sandy clay 25YR3/4 4.2 9.6 43 2.97 25YR4/4 4.5 10.5 38 2.51 25YR3/4 5.0 14.4 38 4.10 7.5YR4/4 6.8 9.6 86 0.00 2.5YR3/4 5.3 18.4 28 0.00 6.4 16.0 60 0.00 60-80 sandy clay abundant 2.5YR2.5/4 4.3 16.8 31 3.65 60-I 10 clayey sand 50-80 sandy clay 75-130 clayey sand 55-120 sandy clay 105-150 clayey sand 2.5YR3/3 4.8 9.6 48 2.75 2.5YR3/4 4.8 14.4 40 4.7 7.5YR4/6 5.1 8.8 49 0.00 5YR3/6 5.5 20.8 28 0.07 7.5YR4/6 6.4 17.6 49 0.00 Horizon I depth cm texture gravel colour PH CEC Base sat. % A13+ meq Horizon 2 depth texture gravel colour PH CEC Base sat. 4% AI”+ 60-105 clayey sand abundant lOYR2,‘I Horizon 3 depth texture gravel colour PH CEC Base sat. % Alj+ a CEC (I M NH,OAc), Al (I M KCI), both in cmol kg-‘, pH (H20) 1:2.5 84 E. Hnhururema. K.G. Steiner/Geodermu 75 (1997) 75-87 three regions, the definition of subtypes may vary and these are only known to experienced, old farmers. The classification is used in the same way by all farmers in the three zones of the study area, even though the natural distribution and relative importance of each soil type vary considerably between the zones. The further division of these subtypes is based on the following criteria (Table 7): - profile depth and soil structure, - degree of hydromorphy, and - colour, iron oxides. 5.6. Comparison of ,farmers ’ and scientists ’ approaches to soil classi$cation In an attempt to make use of farmers’ profound knowledge of soils, possible correlations between farmers’ classification and scientific soil criteria as well as classification systems were investigated. Comparison of the data from reference points on the national soil map and of the soil profiles does not reveal a close correlation between orders and/or groups of the soil taxonomy and farmers’ types (Table 8). This is not surprising, as farmers and scientists pursue different objectives and therefore apply different approaches (Schutjes and Van Driel, 1994). Farmers attempt to describe the suitability for certain production systems of soils of their region. Thus they restrict themselves to the topsoil (A horizon), i.e., the stratum they till and which is exploited by their crops, and apply descriptive names of their own language. Scientists, on the other hand, attempt to characterise soils in a universal manner. They do not limit themselves to soil fertility or the suitability of topsoils. In contrast soil types or soil orders are mainly characterised by diagnostic properties of B horizons reflecting soil genesis as well. Soil scientists also apply a range of physical and chemical parameters to differentiate soils. Even though, in general, there is some correlation between fertility characteristics of the topsoil and the underlying strata, this correlation is lost when soil development in situ is disturbed by erosion and sedimentation. Such discontinuities are very common in the humid tropics and especially in a hilly and mountainous landscape like Rwanda. 6. Conclusions The study reveals a profound indigenous knowledge of arable soils. Farmers proved to be experts in soil suitability classification. However, this does not rule out the possibility of inappropriate management (Pieri, 1989; Sanchez and Van Houten, 1994; Nye and Greenland, 1960 and Coleman et al., 1989). In contrast with most scientific soil classification systems, the local classification system is based on criteria influencing the use and productivity of soils as well as tillage properties, i.e. farmers’ classification corresponds directly to soil suitability. Therefore, the attempt to identify linkages between the indigenous system and scientific soil classification systems gave unsatisfactory results because scientific systems additionally apply other criteria such as genesis of the soil, chemical properties and subsoil characteristics. This corresponds to observa- E. Habarurem, K.G. Steiner/Geoderm 75 (19971 75- 87 85 tions made by other authors in other countries, for example in Burkina Faso or Zambia (Schutjes and Van Driel, 1994; Sikana, 1993). This discrepancy, however, is no reason at all to neglect farmers’ knowledge. Farmers’ soil classification serves the requirements of extension services much more closely than any more or less genetically orientated soil map. Not only do the choice of crops species and varieties and soil management practices correspond better to soil suitability classes than soil series or orders, extension messages can also be more finely tuned. A general problem of all soil maps is the scale, especially in mountainous areas, where soil productivity varies within short distances due to the relief (Steiner et al., 1994). Muchena and Kiome (19951, discussing the role of soil science in agricultural development, claim therefore that the soil resources inventory in East Africa is not adequate for land use planning at regional and farm level. They stress the need for accelerated systematic soil surveys at reconnaissance levels. A systematic use of farmers’ knowledge would allow for a rapid and cheap appraisal of soils of individual fields or even parts of fields and for the site-specific recommendation of management practices and crops. Efforts to improve linkages between research, extension and farmers will only be successful if researchers and extensionists use a simple (local or regional) language that is understood both by farmers and extension field staff. The use of farmers’ indigenous knowledge systems, in this case on soil suitability, would be an ideal means of facilitating dialogue between farmers and agronomists. The precondition for systematic use of farmers’ soil classification is that soils should be classified in the same way by farmers in different villages and districts. This was the case in the three circumscriptions of the study area. No information is available from other regions of the country, however. Comparable studies should be undertaken in those regions. As the same national language is spoken everywhere, there is a great likelihood that at least the major types are evaluated in a comparable way. However, regional differences could be taken into account by the regional extension services without major problems. In addition, most projects are limited to specific regions and will have no problems with variations, for example between North and South Rwanda. It is strongly recommended to use local soil names for the prospective soil suitability map of Rwanda. It can be assumed that traditional farming societies have a more or less detailed soil classification system. Therefore more studies of this indigenous knowledge are necessary with the objective of facilitating exchange between researchers/developers and farmers. At the same time, local knowledge should find its way into school and university curricula. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Acknowledgements This paper is based on a diploma thesis supervised by Prof. Dr. Bernard Mutwewingabo, University of Butare. We are grateful for his advice on structuring farmers’ interviews and on the systematic evaluation of the data. We are also grateful to 86 E. Haharurema. K.G. Steiner/ Geoderma 75 (1997) 75-87 Venant Rutunga, former soils scientist at the National Agricultural Research Institute (ISAR), who revised the draft. We profited from his deep knowledge of Rwanda’s soils and farming systems. In addition, of course we owe thanks to the farmers, who spent their time sharing their knowledge of soils and soil management practices. During the time that this paper was written, all of them suffered heavily from the civil war. While the sad fate of the researchers is known, the events on the hills and farms will never be recorded. The study was supported by the GTZ-executed project “Appui ‘a l’mstitut des Sciences Agronomiques du Rwanda (ISAR)“, which was financed by the German Federal Ministry of Economic Cooperation and Development (BMZ). 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